The invention relates to an internally cooled strand-guiding roll, preferably for a continuous casting installation, having a central rotatable shaft and at least one roll shell which is supported fixed against rotation on this shaft.
Strand-guiding rolls are used in continuous casting installations to support and guide continuously cast metal strands after they have emerged from a permanent mold in a strand-guiding stand. They are exposed to high thermal stresses, since the cast metal strands leave the mold at a temperature of over 1000° C., in particular in the case of steel strands. When producing relatively thick strands, especially in slab formats, a considerable liquid core is also still present in the strand, as a result of which ferrostatic forces act on the strand-guiding rolls. In addition, the strand-guiding rolls have to be able to withstand deformation forces from the strand bending. Accordingly, the strand-guiding rolls are usually equipped with internal cooling and have a robust design which matches the mechanical stresses. Large strand widths of the cast strands of up to 3 m require multiple mounting of the strand-guiding roll, and accordingly a multi-part structure of the supporting strand-guiding rolls.
A number of proposed solutions for the configuration of the internal cooling of a strand-guiding roll are already known from the prior art.
According to one group of proposed solutions, an annular coolant passage or a plurality of flow passages in an annular arrangement are arranged between a roll shell and a central shaft or axle. One general drawback of this embodiment results from the considerable distance between the roll surface and the coolant passages, resulting in excessively high surface temperatures at the roll shell on account of the delayed heat transfer, with the result that additional external cooling is required.
A strand-guiding roll which belongs to this group of strand-guiding rolls is known, for example, from DE-A 25 52 969. This is a strand-guiding roll with a multiply mounted continuous shaft, on which individual roll shells are arranged fixed against rotation by a welded join. An annular space is formed as coolant passage between the central shaft and each roll shell, and this annular space is connected to central supply lines. This welded design does not allow the strand-guiding roll to be dismantled and therefore does not allow the roll shells, which are subject to high thermal and mechanical stresses, to be replaced. Since the coolant passage runs between the shaft and the roll shell, it is at a considerable distance from the roll shell surface, which has an adverse effect on the dissipation of heat from the roll shell. Rather, the roll shell as a whole in fact acts as a heat accumulator.
WO 02/38972 A1, with reference to FIGS. 1a and 1b, reports a prior art which relates to a strand-guiding roll with a central, multiply mounted shaft and a plurality of roll shells arranged thereon. The entire inner surface of each roll shell bears against the outer surface of the shaft and is joined to it fixed against rotation by a feather key. This strand-guiding roll is internally cooled by means of a coolant line which is routed centrally within the shaft. A strand-guiding roll of this type has the fundamental drawback of a particularly long heat transfer path from the shell surface to the coolant line. The assembly-related annular gap between the shaft and the roll shell acts as an insulator and additionally impedes the dissipation of heat from the strand-guiding roll.
Furthermore, WO 02/38972 A1 has disclosed a strand-guiding roll with a multiply mounted shaft and roll shell fitted onto it, each roll shell being arranged fixed against rotation on the shaft by means of a feather key. An annular space, which is filled with a material with a high thermal conductivity, is formed between the roll shell and the shaft over a subregion of the longitudinal extent of the roll shell. The heat is dissipated from the strand-guiding roll by internal cooling via a central coolant line which passes through the shaft. The thermally conductive filler material avoids the barrier action of an air gap between roll shell and shaft, but nevertheless there is still a considerable distance between the thermally stressed roll shell surface and the coolant line.
A strand-guiding roll with a single roll shell and coolant passages of various configurations between the roll shell and the roll core is also known from U.S. Pat. No. 4,442,883.
According to a further group of known proposed solutions, coolant passages are integrated directly in a substantially single-piece roll body, these coolant passages being formed by through-bores. It is in this way possible for the coolant passages to be arranged close to the roll surface and to achieve an increased cooling action by means of the resulting shorter heat transfer path.
Strand-guiding rolls of this type, with coolant bores distributed uniformly close to the roll surface, are already known from WO 93/19874, U.S. Pat. No. 5,279,535 and U.S. Pat. No. 4,506,727. These strand-guiding rolls are formed by a single-piece roll body with bearing journals adjoining it on both sides. The coolant is supplied via a rotary leadthrough, which adjoins the bearing journals at the end sides, and a central supply bore, from which radial branch lines lead to the coolant bores arranged at the roll periphery. A multiplicity of peripheral coolant bores are supplied with coolant from one branch line, with coolant flowing through the strand-guiding roll in alternating directions. The coolant is diverted in annular flanges attached to the end sides of the roll body by means of corresponding diversion passages which connect successive coolant bores to one another. However, single-piece strand-guiding rolls can only be used in continuous casting installations for producing relatively narrow slab strands with a width of up to 900 mm, and for strands with a bloom and billet cross section. In addition, in the event of damage to the roll surface, the single-piece roll requires complex repair work or requires the entire strand-guiding roll to be replaced.
A strand-guiding roll likewise with a single-piece structure of the roll body and therefore restricted possible uses is known from DE-C 33 15 376. Only the distribution of coolant to the peripherally arranged coolant bore takes place selectively, starting from a coolant chamber arranged in the roll body, by means of a control disk which opens up individual coolant bores.